What is the difference between civil twilight, astronomical twilight, and nautical twilight?
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They go one after the other.
In the morning, first comes astronomical twilight, than after that ends nautical twilight starts, when nautical twilight ends, civil twilight starts and that ends with dawn.
In the evening they go in the opposite order: sunset, civil, nautical and then astronomical twilight.
The exact definitions are not based on time before dawn or after dusk or how bright or dark it is but on the position of the sun.
* 0° to 6° below the horizon is civil twilight
* 6° to 12° below the horizon is nautical twilight
* 12° to 18° below the horizon is astronomical twilight
If you get close enough to the poles you may not ever reach dawn or night and just get stuck in one of the twilight phases before going back the other way.
Because the length of those phases depends on how far north/south and time of the year you are (and even how high up you are), some places just define “civil twilight” to mean c minutes before dawn/after dusk. This makes laws easier to write, but can fail to mesh with reality.
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